1. Field of the Invention
The present invention relates to a base station for communications, and more particularly, to a base station using optical communications.
2. Background of the Related Art
FIG. 1 is a conceptual view of a general optical base station. As shown therein, a mobile communication base station 10 transmits a radio signal with sufficient power to reach to every terminal within a service area. However, in view of the characteristics of the radio wave, shadow areas may exist, causing a failure to communicate with a terminal. Shadow areas may be the result of a skyscraper, a rear side of hill areas, or an underground living area. In addition, if a new skyscraper is built, a new shadow area is generated.
In order to provide the shadow area with a communication service, a communication service provider should establish a new base station or operate a small-sized remote base station 100 using the same frequency, data signal, and control signal as those of a pertinent base station. In most cases, in order to effectively operate within a limited frequency spectrum, the remote station 100 is installed. The remote base station 100 is also called an optical base station.
FIG. 2 is a schematic view showing the construction of a signal transmitting apparatus for an optical base station in accordance with the related art. As shown in FIG. 2, the related art signal transmitting apparatus for an optical base station includes a base station 10 controlling a plurality of optical base stations 100 or transmitting and receiving a radio frequency (RF) signal to and from the plurality of optical base stations 100 through an optical connecting unit 70. The optical connecting unit 70 converts the RF signal outputted from the base station 10 into an optical signal and outputs the optical signal through an optical cable 90 to the plurality of optical base stations 100. Additionally, optical connecting unit 70 converts optical signals received through the optical cable 90 into an RF signal and transmits the RF signal to the base station 10. The remote station 100 converts the optical signal received through the optical cable 90 from the optical connecting unit 70 into a high power RF signal used in a mobile communication system and transmits the high power RF signal to an antenna. The remote station 100 down/up-converts the RF signal received by the antenna, converts the converted signal into an optical signal, and outputs to the optical signal optical cable 90.
FIG. 4 is a view showing the construction of the signal transmission apparatus for an optical base station of FIG. 2. Referring to FIG. 4, the optical connecting unit 70 includes a divider 20 receiving the RF signal from the base station IO and dividing it to a plurality of base station connecting units 80. Optical connecting unit 70 also includes a plurality of base station connecting units 80 adjusting a voltage level of a signal outputted from the divider 20, converting the adjusted signal into an optical signal, and transmitting the optical signal through the optical cable 90 to the plurality of optical base stations 100. Each of the base station connecting units 80 also convert the optical signal received through the optical cable 90 to an RF signal, adjust a voltage level of the converted signal, and output it. Optical connecting unit 70 also includes a combiner 60 combining the output signals of each base station connecting unit 80 and outputting it through a single path to base station 10.
The base station connecting unit 80 includes a transmission signal level controller 30 adjusting a voltage level of the signal outputted from the divider 20. Base station connecting unit 80 also includes an optical transceiver 40 converting the output signal of the transmission signal level controller 30 into an optical signal and outputting the optical signal to the optical cable 90, or converting the optical signal received through the optical cable 90 into an RF signal. Base station connecting unit 80 also includes a reception signal level controller 50 adjusting a voltage level of the signal outputted from the optical transceiver 40 and outputting it to the combiner 60.
The optical connecting unit 70 includes a plurality of base station connecting units 80 equal to the number of remote stations 100.
The remote station 100 includes an optical transceiver 120 converting an optical signal received through the optical cable 90 into an RF signal, or converting the RF signal outputted from an down/up converter 170 into an optical signal and outputting the optical signal to the optical cable 90. Remote station 100 also includes an up-converter 130 up-converting the output signal of the optical transceiver 120 into an RF signal used in a mobile communication system and a high power amplifier (HPA) 140 amplifying the RF signal outputted from the up-converter 130 into a high power signal. Remote station 100 also includes a duplexer 150 filtering the output signal of the HPA 140 and outputting it to an antenna 110, or outputting a signal collected by the antenna 110 to a low noise amplifier (LNA) 160, which amplifies the output signal of the duplexer 150. An down/up converter 170 is also provided for down-converting the output signal of the LNA 160, SAW-filtering the down-converted signal, and up-converting it. The operation of the down/up converter 170 is a process for reducing an influence of a different mobile communication service signal.
In a transmission process of the above-described related art signal transmitting apparatus, the RF signal outputted from the base station 10 is divided to multiple optical base stations 100 by the divider 20 and outputted to each remote station 100 connects to base station connecting unit 80. The transmission signal level controller 30 of each base station connecting unit 80 adjusts the output signal of the divider 20 to a suitable voltage level and then applies it to the optical transceiver 40. The optical transceiver 40 converts the applied signal into an optical signal and outputs the optical signal to the optical cable 90 connected to the plurality of remote stations 100.
Upon receiving the optical signal through the optical cable 90, the optical transceiver 120 of the remote station 100 converts the optical signal into a RF signal. The signal outputted from the optical transceiver 120 passes to the up-converter 130, the high power amplifier 140 and the duplexer 150, and then is transmitted through the antenna 110 to a corresponding terminal.
The operation of the reception signal transmitting apparatus for an optical base station will now be described in detail with reference to FIG. 4. The RF signal outputted from the base station 10 is transmitted to the divider 20 of the optical connecting unit 70, and the divider 20 divides the RF signal into a plurality of base station connecting units 80. The transmission signal level controller 30 of each base station connecting unit 80 adjusts the divided RF signal to a suitable level and transmits it to the optical transceiver 40. The optical transceiver 40 converts the received RF signal into an optical signal and transmits the optical signal through the optical cable 90 to a pertinent remote station 100.
The optical transceiver 120 of each remote station 100 converts the optical signal received through the optical cable 90 into an RF signal and outputs the RF signal to the up-converter 130. The up-converter 130 up-converts the received signal into an RF signal for use in a mobile communication system and outputs it to the HPA 140. The HPA 140 amplifies the inputted signal to a high power signal and transmits the high power signal through the duplexer 150 to the antenna 110.
A signal collected by the antenna 110 is applied to the LNA 160 by the duplexer 150, and the LNA 160 amplifies the applied signal and transmits it to the down/up converter 170. The down/up converter 170 down-converts the inputted signal, then up-converts the down-converted signal by performing a SAW-filtering thereon, and outputs a resulting signal to the optical transceiver 120. The optical transceiver 120 converts the output signal of the down/up converter 170 into an optical signal and transmits the optical signal through the optical cable 90 to the base station connecting unit 80 of the optical connecting unit 70. The optical connecting unit 70 includes one base station connecting unit 80 for each remote station 100.
The optical transceiver 40 of the base station connecting unit 80 restores the optical signal received through the optical cable 90 to an RF signal. Reception signal level controller 50 adjusts the restored RF signal to a suitable voltage level and outputs it to the combiner 60. The combiner 60 combines the output signals of each base station connecting unit 80 and transmits it to the base station 10.
FIG. 3 is a drawing illustrating a signal transmitting apparatus for an optical base station adopting an E2DM method in accordance with a different related art. As shown therein, when an RF signal outputted from the base station 10 is transmitted to the optical connecting unit 75, a transmission signal level controller 35 of the optical connecting unit 75 adjusts a voltage level of the received RF signal and outputs it to an optical transceiver 180. Then, the optical transceiver 180 converts the inputted RF signal into an optical signal and applies the optical signal to an optical distribution unit 190. The optical distribution unit 190 distributes the applied RF signal to a plurality of remote stations 105 through the optical cable 90.
The optical transceiver 200 of the remote station 105 converts the distributed optical signal into an RF signal and outputs the RF signal to a transmission signal level controller 230, and the transmission signal level controller 230 adjusts the inputted signal to a suitable voltage level and applies it to an HPA 140. The signal applied to the HPA 140 is amplified to a high power signal and transmitted through a duplexer 150 and an antenna 112 to a terminal.
Meanwhile, a radio signal of the terminal is collected by the antennas 112 and 114, and the collected signal is transmitted to the base station 10 though two paths performing a receiving process. The antennas 112 and 114 are diversity antennas for preventing a fading phenomenon of a received signal, and are separately disposed to maintain an optimum distance there between in consideration of a wave length. The RF signal collected by the antennas 112 and 114 is outputted to each LNA 160 and 160′ by duplexers 150 and 150′, amplified by the LNAs 160 and 160′, and transmitted to notch filters 210 and 210′. The notch filters 210 and 210′ removes a noise of a certain band from the received signal and outputs the signal without a noise to reception signal level controllers 220 and 220′. The reception signal level controllers 220 and 220′ adjust a voltage level of the inputted signal and apply it to the optical transceiver 200. The optical transceiver 200 converts the applied signals of the two paths into an optical signal and outputs it to the optical cable 90.
The signal outputted to the optical cable 90 is transmitted to the optical distributor 190 of the optical connecting unit 75. The optical distributor 190 combines the optical signals outputted from the plurality of remote stations 105 and applies the combined signal to the optical transceiver 180. The optical transceiver 180 converts the applied optical signal into an RF signal and divides it into two paths for outputting. The signal outputted from the optical transceiver 180 is inputted into the reception signal level controllers 55 and 55′, adjusted to have a suitable voltage level, and transmitted to the base station 10.
The above-described related art signal transmitting apparatus for a remote station can be used with a 3 wave division multiplexing (3WDM) method. Unlike the signal transmitting apparatus for an optical base station of the related art in which the optical connecting unit 70 includes the plurality of base station connecting units 80, the 3WDM method operates an optical connecting unit 75 with only one optical distribution unit 190 and uses a diversity antenna.
As noted, in the above two embodiments, the optical connecting unit 70 and the remote stations 100 and 105 are based on an analog interface for processing the RF signal.
The related art signal transmitting apparatus for an optical base station has many problems and disadvantages. For example, in the apparatus of FIGS. 2 and 4, as the RF analog signal is converted into an optical signal and is passed through the optical transceivers 40 and 120, the reception performance is degraded and the level of a noise signal is heightened. In order to solve the problem, the gain characteristic of the LNA 160 can be improved, but in view of the input limitation characteristic of the optical transceivers 120 and 40, any improvement will be marginal. Likewise, the apparatus of FIG. 3 solves the problem of fading by receiving a signal of a terminal in the diversity method, but it fails to solve the problem that the reception signal is degraded as a consequence of analog signal processing.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.